Bow drill

The bow drill is a prehistoric form of drilling tool. It commonly was used to make friction fire, and in this function it also was called a fire drill. However, the same principle also was used widely in drilling for purposes of woodworking and dentistry.

Bow drills were used in Mehrgarh between the 4th and 5th millennium BC. This bow drill—used to drill holes into lapis lazuli and carnelian—was made of green jasper. Similar drills were found in other parts of the Indus Valley Civilization and Iran one millennium later.

The bow drill consists of a bearing block or handhold, a spindle or drill, a hearth or fireboard, and a simple bow. Other early versions of mechanical drills include the pump drill and the hand drill.

The drill offers an ancient method of starting fire without matches or a lighter, a method that applies friction to generate heat. The heat eventually produces an ember in the burnt sawdust. The ember is tiny, smaller than the head of a cigarette, and fragile. Once the ember is formed it is carefully placed into a "tinder bundle" (a bird's type nest of stringy, fluffy, and combustible material). Once the ember is in the tinder bundle it is then carefully nurtured and coaxed into flame. Once the tinder bundle bursts into flame, it is placed into the fuel that has been assembled ready for ignition.

The spindle, carved to reduce friction at one end and maximize it at the other, is held in a hole in the bottom of the bearing block, and at the other by the base board (which also is known variously as the hearth, hearth board, or fireboard). The string of the bow is wrapped once around it, so that it is tight enough not to slip during operation. A variation on this is called the "Egyptian Bow Drill", which attaches the string by wrapping it around multiple times, or actually tying it to the drill or through a hole through the drill shaft, then wrapping it.

The usual position that a person assumes whilst operating the bow drill is as follows: the right knee is placed on the ground (assuming a right-handed operator) and the arch of the left foot is on the board, pinning it in place. The left wrist, holding the handhold, is hooked around the left shin and locked in place to keep it steady so it can generate enough downward pressure and speed; achieved by pushing down with the handhold and spinning the drill. The heat of the friction between the hearth and the spindle both creates charred, fuzzy dust and causes it to ignite - forming a coal or ember. The handhold is lubricated and the spindle is carved to about thumb thickness, usually 6 to 8 inches (150 to 200 mm) long. Another option to practice is to make the "handhold" into a "mouth-hold" piece, so it's held down by pressure from the chin/mouth, leaving both hands free.

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